1. Field of the Invention
The invention relates to a device for comminuting feedstock.
2. Description of the Background Art
The comminuting of feedstock is a central component of mechanical process engineering in which a starting material is divided by separation into smaller parts. In this case, the feedstock is altered in its size, form, or composition in view of its later use. Separation methods suitable for this provide for comminuting by means of tearing, beating, rubbing, grinding, or cutting. An example is the preparation of waste products, in which size reduction of the feed material is a requirement for processing in subsequent processing stations or in which separation into various components, present in the feedstock, occurs simultaneously during comminuting.
It is known for comminuting by means of cutting to move the cutting edges of cutting tools past one another to execute an effective motion. Apart from the type of feedstock and its insertion during the cutting process, the cutting geometry determined by the machine structure as well is a major determining factor for the cutting process. To achieve a clean cut, it is necessary in particular that the active cutting edges of the cutting tools slide past one another while maintaining an optimal blade clearance, which depends on the type of feedstock. With an increase in the distance between the jointly acting cutting edges, the effectiveness of the cutting process declines, because part of the energy to be applied for grinding, tearing, or crushing the feedstock is used up. As a result, increased mechanical stress arises, which accelerates signs of wear, reduces operating reliability, and not least increases energy consumption. Maintaining an optimal cutting geometry is very important therefore.
U.S. Pat. No. 4,684,071 discloses a device for comminuting used tires, in which a vehicle tire is divided by counter-rotating cutting rotors. The cutting rotors including cutting discs which are arranged on a shaft at an axial distance and are populated at their circumference with cutting tools, whereby the cutting discs of the one rotor engage with a smaller radial overcutting into the gaps of the other cutting rotor. Because the cutting tools are exposed to great mechanical stress during operation and have a correspondingly great wear, the cutting tools are affixed detachably to the cutting discs, so that they can be replaced by new or resharpened tools.
Two possible ways of affixing the cutting tools to the cutting discs are disclosed in U.S. Pat. No. 5,730,375. It is possible, on the one hand, to form the circumferential surface of each cutting disc in the shape of a polygon, which results in a planar support surface for the cutting tools. The cutting tools are bolted down by means of radially acting bolts, which are accessible from the top side of the cutting tools and extend into the circumferential area of the cutting discs, whereby the heads of the bolts come to lie within corresponding recesses. Because during damage to cutting tools due to rough comminuting operation the support surface for the cutting tools and the tapped holes in the cutting discs become damaged and must be repaired when the cutting tools are changed, another embodiment, depicted in U.S. Pat. No. 5,730,375, comprises affixing the cutting tools with the interconnection of a bearing plate on the outer circumference of the cutting discs. This has the advantage that in the case of damage only the bearing plates need to be replaced but the entire support surface of the cutting discs need not be resharpened. In addition, to take up the fixing bolts bushings are provided, which have both an inside and outside thread and are screwed into radial holes in the disc rotor. With their inside threads, the bushings in turn take up the fixing bolts. If an inside thread is damaged, the threaded bushing can be replaced as a whole unit without having to work on the disc rotor itself.
During operation of comminuting devices of this type, large axial forces arise, which are passed via the cutting tools to the cutting discs. These forces must be absorbed by the fixing bolts, which are stressed thereby by shearing and bending. Because the load bearing capacity of each bolt is limited, the removal of the total load requires a relatively large number of fixing bolts, which, when the cutting tool is changed, entail a correspondingly large amount of work because of their loosening and retightening.
Another factor is that the positioning of the cutting tools on the cutting discs is carried out with the fixing bolts. As a result of the play between the cutting tool and the fixing bolt, large tolerances arise during the setting of the blade clearance, which are an obstacle to maintaining a precise cutting geometry and entail the previously described negative effects on the cutting process.
Another factor is that based on geometric circumstances and static requirements, the fixing bolts may be disposed only with maintenance of a minimum distance to the transverse edge of the cutting tools. The arising leverages with a nonuniform load application during the comminuting process lead to a nonoptimal load removal, which must be considered in dimensioning the fixing bolts.
To find a remedy here at least in part, European Pat. No. EP 1 289 663 A1, which corresponds to U.S. Publication No. 20030122006, and which discloses a rotor for a generic comminuting device, in which the cutting tools are affixed laterally to a tool holder by means of screws, optionally with the interconnection of compensating plates. The thus arising cutting unit comprising tool holder and cutting tools is affixed by radially acting screws at the outer circumference of a cutting blade, whereby positioning pins are provided for exact positioning of the cutting unit. As a result, the positioning accuracy of the tool holder relative to the cutting disc is in fact improved, but dimensional inaccuracies are again introduced into the system by the screwing of the cutting tools to the tool holder, optionally with inserted distance plates; these in turn undo this advantage.
In view of the static load removal behavior, in this type of construction, axial stress is introduced via the fixing screws and the positioning pins into the cutting discs with a load removal cross section limited by the number and diameters of the screws or pins. In addition, here as well no optimal force transfer from the cutting tool to the cutting disc is possible, because the positioning pins due to construction must also maintain a minimum distance to the transverse edges of the tool holder.